A terminal provided with a Sn layer (reflow Sn plating or the like) on the surface of a copper or a copper alloy base material is used as a fitting terminal used for connection of electrical wiring of automobiles and consumer appliances in order to secure corrosion resistance and reduce contact resistance at a contact part. When a male terminal and a female terminal, each having a Sn layer formed thereon, are fitted together, deformation resistance occurs due to plastic deformation of the soft Sn layer, and shear resistance occurs due to shearing of adhesion parts between Sn and Sn of the male terminal and the female terminal. Because of this, an insertion force of the terminal enough to overcome such deformation resistance and shear resistance is required. In recent years, with higher functionality and multifunctionality of electronic devices, the number of poles of a terminal used in a connector has increased. Along with this, the insertion force of the terminal has been becoming larger. From the viewpoint of reducing a load on an operator and preventing errors in fitting, it is necessary to reduce the insertion force of the fitting terminal.
Meanwhile, when a printed circuit board and a terminal are joined together by soldering, Pb-free solder has been used to comply with recent regulations on environmentally hazardous substances. However, the Pb-free solder has a melting point higher than conventional Sn—Pb-based solder and exhibits less wettability, leading to low joint reliability in the conventional Sn-plated terminals. For this reason, terminals with excellent solder wettability are needed.
Patent Document 1 describes an electrically conductive material for a connection component in which a coating layer formed of a Ni layer, a Cu—Sn alloy layer, and a Sn layer in this order is formed on a surface of copper or a copper alloy base material. By restricting a thickness of the Sn layer to 0.5 μm or less, the electrically conductive material for a connection component reduces a coefficient of friction and thereby can reduce the insertion force to a low level. Patent Document 2 describes an electrically conductive material for a connection component in which a coating layer formed of a Ni layer (if necessary), a Cu—Sn alloy layer, and a Sn layer in this order is formed on a surface of copper or a copper alloy base material that has a large surface roughness. The Cu—Sn alloy layer has a Cu content of 20 to 70 at %, and an average thickness of 0.2 to 3.0 μm, and the Sn layer has an average thickness of 0.2 to 5.0 μm. The surface of the electrically conductive material has an arithmetic mean roughness Ra in at least one direction of 1.5 μm or more, and an arithmetic mean roughness in all directions of 3.0 μm or less. Parts of the Cu—Sn alloy layer are exposed from the outermost Sn layer, and an exposed area ratio thereof is 3 to 75%. The electrically conductive material for a connection component has a low coefficient of friction and thereby can reduce the insertion force of the connector.
Patent Document 3 describes an electrically conductive material for a connection component in which a coating layer formed of a Ni layer (if necessary), a Cu—Sn alloy layer, and a Sn layer in this order is formed on a surface of copper or a copper alloy base material. The Cu—Sn alloy layer has an average thickness of 0.2 to 3.0 μm, and a glossy or semi-glossy Sn plating layer with a uniform thickness is formed as a part of the Sn layer, in the outermost layer. When viewing the cross section perpendicular to the material surface, the diameter [D1] of the minimum inscribed circle of the Sn layer is 0.2 μm or less, the diameter [D2] of the maximum inscribed circle of the Sn layer is 1.2 to 20 μm, and the height difference [y] between the outermost point of the material and the outermost point of the Cu—Sn alloy layer is 0.2 μm or less. The electrically conductive material for a connection component has a low coefficient of friction, can reduce the insertion force of the connector, and exhibits excellent solder wettability.